392 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 1() 



The use of gnomonic projection in studying Laue photographs is mentioned 

 and a ruler is described, the use of which reduces the time and labor of making 

 such projections. The effect of the voltage impressed on the X-ray tube upon 

 the character of the Laue photograph is considered and the best conditions 

 for operating a tungsten tube for this work are stated. R. W. G. W. 



PETROLOGY. — The rhyolites of Lipari. Henry S. Washington. Amer. 

 Journ. Sci. 50: 446-462. 1920. 

 Typical obsidians, pumice, lithoidal rhyolite, and a hyalo-dacite of Lipari 

 are described, with six new analyses. As these rhyolites are regarded as typi- 

 cal and have never before been completely analyzed, this work is of use in 

 characterizing the type. The refractive indices of the obsidians and pumice 

 are discussed. There is also given an analysis of an obsidian of the island of 

 Milos, of which the refractive index was also determined. The data corre- 

 spond well. This is compared with analyses of obsidian of Nisyros by Martelli. 

 The observation is made that ferrous oxide dominates ferric oxide in the 

 glassy forms of the same magma, while the converse is true of the crystalline 

 forms in the Lipari rhyolites. The same holds good for the rhyolites of Sar- 

 dinia and the pantellerites and basalts of Pantelleria, described some years 

 ago by the writer. The possible relation of this to the magmatic gases in 

 lavas is briefly discussed. H. S. W. 



GEOLOGY.— 7/z^ potash deposits of Alsace. H. S. Gale. U. S. Geol. 

 Survey Bull. 715-B. Pp. 39, pis. 2, figs. 2. 1920. 

 The discovery of potash in Alsace in 1904 broke the monopoly of the potash 

 industry which since 1860 had rested with the producers in north-central 

 Germany. The return of Alsace to France now divides the monopoly between 

 two nations. The new field, although of less extent, is in some ways better 

 than the older field ; the beds are very regular, and the salts average remarka- 

 bly high in potash. The deposits, which were discovered accidentally in 

 boring, underlie an area of 65 square miles beneath the valley of the Rhine in 

 southern Alsace. They consist of two regular beds of sylvinite, a simple 

 mixture of potassium and sodium chlorides, included in dolomitic grayish 

 shale of middle Oligocene age. The writer believes that the beds were de- 

 posited by evaporation in an inland salt-lake in the Rhine graben, which 

 probably had no connection with the sea. Forste estimated the reserve of 

 the field as 300,000,000 tons of pure potash, but by no means all of this can 

 be recovered in mining. The crude salt mined in 1913 is reported as 350,341 

 tons, probably averaging 18 per cent in pure potash. J. D. Sears. 



GEOLOGY. — A deposit of manganese ore in Wyoming. Edward L. Jones, 

 Jr. U. S. Geol. Survey Bull. 715-C. Pp. 3. 1920. 

 One of the few manganese deposits known in Wyoming is on the western 

 flank of the Laramie Mountains, near the head of Sheep Creek. The core 

 of the Laramie Mountains is a coarse-grained red granite of pre-Cambrian 

 age, but flanking it on the west side is a series of sedimentary rocks ranging 

 in age from Carboniferous to Cretaceous. The manganese deposit is inter- 

 bedded in limestone and sandstone of the Casper formation, of Carboniferous 

 age. The ore consists of the manganese oxides manganite and pyrolusite, 

 in mammillary crusts and nodular aggregates, and is unusual for its number 

 of crystals. It is contained in two beds of chert a few feet apart, from which 

 it is thought to have been derived by weathering and leaching. J. D. Sears. 



